Urethral bulking agents are a minimally invasive treatment of stress urinary incontinence; they are thought to work by causing reactivity in local tissues leading to permanent integration of the bulking agent into the urethral submucosa, thereby increasing urethral resistance. By nature, they are space-occupying and can often be visualized on a variety of imaging modalities. However, our study determined that bulking agents are incorrectly characterized more than 75% of the time. Furthermore, the presence of a bulking agent was either not mentioned despite being identifiable upon imaging or incorrectly identified as pathologies such as bladder stones, nonspecific calcifications, radiodense material, or urethral stones. This mischaracterization can lead to patient anxiety and/or unnecessary evaluation and intervention, particularly in light of legislation that gives patients early access to their medical records.

A similar phenomenon was noted with use of dextranomer/hyaluronic acid copolymer (Deflux) for treatment of vesicoureteral reflux in children in a study by Cerwinka et al. which described the bright appearance of Deflux implants on T2-weighted MRI imaging done after the procedure [5]. However, to our knowledge, there are few publications related to this phenomenon in urethral bulking agents: a pictorial essay published by Bridges et al. in 2004, a study by Gaines et al. in 2018, and two case reports highlighting difficulty differentiating urethral bulking agent from periurethral diverticula and PET-avid lesions, respectively [2, 3, 6, 7]. The pictorial essay aimed to characterize the radiographic, CT, and MRI appearance of some urethral bulking agents due to their expanding clinical use as treatment for stress urinary incontinence and the assumption that radiologists would be expected to recognize their imaging features in multiple modalities in order to avoid diagnostic pitfalls [3]. Their description of bulking agents on CT included the following: bovine collagen agents have variable appearance on CT as collagen is avascular and the appearance depends on the density of surrounding tissues; carbon-coated microbeads (old-formulation of Durasphere®) appear at least as dense as cortical bone on CT; graphite coated microbeads (new-formulation of Durasphere®) appear less-dense on CT and mimic the appearance of medullary bone [3]. This study does not detail the appearance of newer bulking agent formulations such as Macroplastique® and Urolastic® (silicone), Coaptite® (calcium hydroxylapatite), or Bulkamid® (polyacrylamide). Detailed characterization of the appearance of these bulking agents on various imaging modalities is an important opportunity for future investigation.

Years later, Gaines et al. reported high rates of mischaracterization of bulking agents on subsequent abdominopelvic imaging, which they attributed to omission of the bulking agent from the patient-specific medical history provided to radiologists in the imaging order [2]. This context is critical to appropriate diagnosis and characterization of bulking agents, as they otherwise appear as vague space-occupying or calcified material. It was theorized that this dilemma would resolve with the near-universal adoption of electronic medical record systems which would create a centralized route for reporting patient medical and surgical histories to radiologists when ordering imaging. However, our study demonstrated that this was not the case, as urethral bulking agents continue to go unnoted or mischaracterized.

The profound paucity in literature discussing the frequent mischaracterization of urethral bulking agents may contribute to the persistence of this trend [2, 3]. In order to avoid the pitfall of mischaracterizing urethral bulking agents, it will be important to raise awareness of urethral bulking agents among radiologists both to increase the accuracy of diagnosing the presence of bulking agents and mitigate the anxiety and potentially unnecessary testing for patients. In addition, it is the responsibility of physicians who perform injection of urethral bulking agents to inform patients that their bulking agent will be visible on imaging when appropriate. Length of time between treatment and subsequent imaging may have contributed to the mischaracterization of bulking agents; as based on patient communication following imaging, many of the patients simply forgot they had a urethral bulking agent. Furthermore, following injection of a urethral bulking agent, clinicians need to ensure that patients understand that the bulking agent may be present and identifiable on imaging indefinitely.